1. Field of the Invention
This invention relates to a magnet holder for an electromagnetic diaphragm pump, and particularly to a magnet holder for an electromagnetic diaphragm pump with improved efficiency.
2. Description of the Prior Art
A conventional electromagnetic diaphragm pump is described by using the drawings. FIG. 15 is a cross-sectional view when the conventional electromagnetic diaphragm pump is seen from the front thereof, FIG. 16 is a plan view of the diaphragm pump of FIG. 15, and FIG. 17 is a side view along the X--X line of FIG. 16.
In these figures, a housing 1 is made by the press operation of a metal plate and each of side plates 1A is punched with a circular hole 1B, the side plates being bent at both ends thereof so as to oppose each other.
A pair of diaphragm plates 2 made of an elastic material such as rubber are fitted into the circular holes 1B, respectively. The peripheral portion of each diaphragm 4 is pinched by and between corresponding the diaphragm plate 2 and a head cover 3, which are attached to the side plate 1A of the housing 1 using screws 18.
A pair of plate-like magnets 8 are held in a plate-like magnet holder 6 which is a part of an electromagnetic diaphragm pump and preferably formed of a material such as aluminium. The pair of diaphragm 4 are attached to both ends of the magnet holder 6 by using pressing tools 5 and screws 7. The magnet holder 6 and magnets 8 constitute the vibrator of the electromagnetic diaphragm pump.
Inside each head cover 3, a diaphragm chamber 3A is formed. On each diaphragm chamber 3A, there are formed an intake port 14A and a discharge port 15A, which are provided with an intake valve 14 and a discharge valve 15, respectively.
Each field core 9 is an iron core of laminated silicon steel plate in the shape of "E", and, as shown in FIG. 16, the central leg thereof is fitted in a coil 11 wound around a bobbin 10.
The electromagnetic diaphragm pump is provided with two such field cores 9, which are fixed to the bottom of the housing 1 using bolts 12 and nuts 13 so as to sandwich the magnet holder 6. Since it is needed to support the field cores 9 apart from the bottom of the housing 1 by a predetermined distance, a sleeve 16 is passed through with the bolt 12 as shown in FIG. 17.
Such electromagnetic diaphragm pump is attached through, for instance, rubber vibration insulators 19, to a fluid tank 20 as seen in FIG. 15. A pressurized fluid such as air is discharged into the tank 20 as shown by an arrow C via a tube 17 connected to the head cover 3.
FIG. 18 is a schematic plan view for showing the operation principle of the electromagnetic diaphragm pump. In FIG. 18, the symbols same as those in FIG. 15 or FIG. 17 indicate the same or identical portions.
A pair of magnets 8 attached to the magnet holder 6 are arranged, as shown, so that the magnetic poles of the pair of magnets 8 are reverse to each other. Accordingly, if the coil is supplied with an a.c. current so that a magnetic flux passes from one field core 9 to the other field core 9 in the direction of a solid arrow P or a dotted arrow Q, the magnet holder 6 is reciprocated in the direction of an arrow R by the attractive and repulsive actions between the magnets 8 and a magnetic flux P or Q, whereby the diaphragm 4 is vibrated.
As a result, as shown in FIG. 16 by an arrow A, a fluid is sucked into the diaphragm chamber 3A through the side plate 1A of the housing I, an opening 1D formed in the diaphragm plate 2 and bead cover 3, the intake port 14A and intake valve 14, and the fluid passes through the discharge port 15A and discharge valve 15 as shown by the arrow B and then the fluid is discharged from the tube 17 into the fluid tank 20 as shown by the arrow C in FIG. 15.
Such electromagnetic diaphragm pump is described in, for instance, the Japanese Patent Laid-open Publication No. Showa 61-252881 and the Utility Model Laid-open Publication Nos. Showa 63-100682 and 61-137892.
Various proposals have been made for improving the efficiency of the electromagnetic diaphragm pump.
In the Japanese Utility Model publication No. Showa 56-42448, a technique is disclosed for preventing an eddy current from occurring in the magnet holder 6 by completely removing the bridge portion 6A (FIG. 15) of the magnet holder 6 for holding a pair of magnets 8 which is between the magnets 8, in other words, by inserting a pair of magnets into a single common window by preventing the occurrence of the eddy current, the heat due to the eddy current is not generated in the holder even if the magnet holder is made of a conductive material, so that the electromagnetic energy loss of the electromagnetic diaphragm pump can be reduced and the efficiency thereof can be improved.
The Japanese Laid-open Utility Model Publication No. Showa 63-134179 discloses a technique in which the slits extending in the vibration direction of the magnet holder 6 are provided in both side portions 6B (FIG. 15) for preventing the occurrence of an eddy current.
In each prior art described above for preventing the occurrence of the eddy current, the bridge portion of the magnet holder between a pair of magnets is removed, or the slits are provided in both side portions of the magnet holder along the vibration direction. With such construction, since the mechanical strength of the magnetic holder is decreased, when a large stress is applied to the magnet holder by a strong magneticfield generated from the field cores which are arranged opposite to the magnets, the magnet holder can curve and, thereby, the ideal vibration of the magnet holder may be prevented.
That is, as shown in FIG. 18, a strong alternating magnetic field is generated between the pair of field cores 9 opposing to the pair of magnets B supported by the magnet holder 6, and the vibrator is made to reciprocate by the interaction of the above mentioned magnetic field with the magnetic fields produced from the magnets 8, but, since the vibrator is supported only by the diaphragms 4 formed of a flexible material such as rubber, it can be biased toward one of the field cores 9 during the reciprocating motion.
By the bias toward one of the field cores 9, a torsional force is produced in the magnet holder 6. As previously described, if the magnet holder 6 lacks the bridge portion 6A between the pair of magnets or the slits are provided in both side portions 6B of the magnet holder 6, the magnet holder 6 can twist because of its shortage of the mechanical strength, and thereby a normal reciprocating motion of the vibrator is prevented.
In addition, by this twist, the bonding agent fixing the magnet 8 to the magnet holder 6 may peel off whereby the magnets 8 may be disengaged from the magnet holder. As a result, the durability of the electromagnetic diaphragm pump will be reduced.